"Default displacement = 0, consider adjusting" Error when applying materials
I'm new at this too, I had the same issue today and I spent 30 minutes figuring out what's going on. I see you're using the Poliigon nodes too.

No matter how much I tweaked the actual Displacement node, nothing was displaced.
I only saw the sliders under 2 after half an hour, displacement was visible after moving the Displacement Strength to something else than 0, see my rendered view in the screenshot.

However, I see you don't actually have those sliders in your material custom block. Does your texture have a displacement map in it's folder? Maybe you didn't include it in your download?